ANN ARBOR, Mich.--- How do adult stem cells protect themselves from accumulating genetic mutations that can lead to cancer?
For more than three decades, many scientists have argued that the "immortal strand hypothesis" - which states that adult stem cells segregate their DNA in a non-random manner during cell division -- explains it. And several recent reports have presented evidence backing the idea.
But in this week's issue of the journal Nature, University of Michigan stem cell researcher Sean Morrison and his colleagues deal a mortal blow to the immortal strand, at least as far as blood-forming stem cells are concerned.
They labeled DNA in blood-forming mouse stem cells and painstakingly tracked its movement through a series of cell divisions. In the end, they found no evidence that the cells use the immortal-strand mechanism to minimize potentially harmful genetic mutations.
"This immortal strand idea has been floating around for a long time without being tested in stem cells that could be definitively identified. This paper demonstrates that it is not a general property of all stem cells," said Morrison, director of the Center for Stem Cell Biology at the U-M Life Sciences Institute.
It remains possible that stem cells in other tissues use this process.